1. Field of the Invention
This invention relates to a safer process of loading a hydrogen halide onto an adsorbent and using that adsorbent in a process for removal of impurities from liquid hydrocarbons. More specifically, this invention relates to the removal of lead impurities from hydrocarbon streams.
2. Description of the Prior Art
The ability to remove impurities from hydrocarbon streams is extremely important in the petrochemical and refining industries for both cost and environmental reasons. Impurities in hydrocarbon feedstocks can cause catalyst poisoning of those catalysts used in the manufacturing process. The poisoning of the catalysts necessitates the costly replacement or premature regeneration. The greater convenience of this invention makes it easier to remove lead impurities in accordance with tightening environmental regulations.
There are several ways to remove lead from liquid hydrocarbons, including gasoline. For example, cupric chloride impregnated on nongraphitic carbon or on silica gel can be used for removing lead contamination; A. A. Zimmerman, G. S. Musser et al., SAE Fuels and Lubricants Meeting. (Houston Jun. 3-5, 1975) Technical Paper; Chemical Abstracts vol. 85-1976, 49026 G. Strongly acidic cation exchangers can be used to remove lead (German Pat. DT No. 2,361,025). SiCl.sub.4, CuCl.sub.2, CuBr.sub.2, I.sub.2, or I.sub.2 combined with an acid, can be used to pretreat a hydrocarbon, which is then followed by contacting step with activated carbon and an acid treated clay or silica gel to remove lead (U.S. Pat. No. 3,893,912). Aqueous sorbents can be used to remove lead contaminants from gasoline as taught by U.S. Pat. No. 2,368,261 (Neef). However, large amounts of lead, as much as 0.20 gm per gallon (approximately 70 parts per million (ppm)), remain after the treatment.
More effective technology, which is also more dangerous, is disclosed in U.S. Pat. No. 4,424,120 (Audeh), utilizes hydrogen chloride in a process which reduces lead levels in gasoline to less than 0.20 gm per 16,000 gallons (0.004 ppm). However, the adsorbent preparation procedure disclosed by Audeh requires passing 100% anhydrous hydrogen chloride through an adsorbent column until the adsorbent is sufficiently saturated with this dangerous acid. Such an operation requires serious safety precautions.
Anhydrous hydrogen chloride is a colorless gas with a sharp, pungent odor. On contact with the moisture in air, it forms dense poisonous fumes of hydrochloric acid which requires special handling. Due to these dangers, the Occupational Safety and Health Association (OSHA) has placed a ceiling limit on hydrogen chloride of 5 molar ppm on a time-weighted average exposure limit (ACGIN, 1984-85). and requires that it be used only in well-ventilated areas to prevent accumulation above this ceiling limit. It is irritating and corrosive to the upper and lower respiratory tracts, skin and eyes. Internal symptoms include tearing, coughing, labored breathing, and excessive salivary and mucous formation. Excessive irritation of the lungs causes acute pneumonitis and pulmonary edema, which could be fatal. Hydrochloric acid burns exhibit severe pain, redness, possible swelling and early necrosis.
Because of these dangers, special protective equipment is required on a routine basis, including chemical gloves, and safety goggles or face shield. In the event of a spill or release of hydrogen chloride, a general evacuation of all people in the area is required. Emergency personnel require additional special protective equipment, including positive-pressure air lines with mask or self-contained breathing apparatus.
Hydrogen chloride attacks metals as well as people, as it is very corrosive to metallic process equipment. Special precautions must be taken to ensure the hydrogen chloride does not get contaminated with moisture as most metals corrode rapidly when in contact with wet hydrogen chloride. Plant equipment utilizing hydrogen chloride must employ very costly acid resistant materials, such as stainless steel or rubber-lined carbon steel. For example, stainless steel costs five times what carbon steel costs.
Because of these safety and cost considerations, it is prohibitive to use hydrogen chloride for large-scale operations. The other hydrogen halides, such as hydrogen bromide (HBr.sub.2), hydrogen floride (HF.sub.2), and hydrogen iodide (HI.sub.2), have similar characteristics to hydrogen chloride since they are also strong acids.
The present invention provides a very safe and cost effective way to load the hydrogen halide onto an adsorbent. This invention may remove more of the lead from liquid hydrocarbon than other methods. This new process can reduce the lead contamination in a raffinate feedstock of 44 ppm to less than 1 ppm.